Grain size distribution of pedogenic magnetic particles in Chinese loess/paleosols

Variations in magnetic parameters of the long Chinese loess/paleosol sequences reflect paleoclimatic fluctuations. However, there remain ambiguities whether the magnetic proxies are controlled by the concentration or by the distribution of magnetic grain sizes. We systematically investigated the frequency-dependence of low-field magnetic susceptibility (chi(fd)%) and the decay-rate (DR) dependence of anhysteretic remanence magnetization (ARM) susceptibility (chi(ARM, DR)%) for a set of representative loess/paleosol samples from the Yuanbao section, western Chinese loess plateau. After removing the effect of aeolian coarse-grained magnetites, both chi(fd)% and chi(ARM, DR)% are nearly independent of the degree of pedogenesis, indicating a presence of fine-grained magnetic particles ranging from superparamagnetic to single domain with an almost constant grain size distribution. Therefore, the magnetic enhancement of magnetic susceptibility or ARM is caused dominantly by changes in the concentration of these fine-grained pedogenic grains.